1. Field of the Invention
The present invention relates to side loading specimen grips that are hydraulically actuated without causing any substantial movement of the specimen during clamping and which eliminates undesirable bending moments during specimen testing.
2. Description of the Prior Art.
In the prior art, various specimen grips have been advanced. Self aligning and hydraulically actuated grips are shown in U.S. Pat No. 3,335,603 issued to Martin M. Gram, on Aug. 15, 1967. In this patent the actuator cam for the grips is a cylindrical member and the specimen was to be installed from the end of the grip. Additionally, this patent shows a self aligning head connection to the actuator exerting the load on the specimen.
U.S. Pat No. 3,224,259 shows a typical side loading mechanically actuated grip for tensile testing only, wherein there is longitudinal motion of the jaws relative to the grip during tension testing of the specimen. A specimen can be loaded into this mechanical grip from a front side only--the grip has a back portion connecting its two side grip pieces. Thus, as the grip is actuated, the grip force is uneven across the specimen from front to back because the side grip pieces which act on the specimen grip jaws act as cantilevers. The clamping force on the specimen is greater adjacent the back of the grip than near the front. This uneven force or distortion of the clamping force can place a bending moment on the specimen and thereby influence the specimen test results, especially with a specimen of relatively brittle material. The present device permits side loading of a specimen, and in particular flat plate-like specimens, and has actuated jaws that move only transverse to the longitudinal axis of the specimen, thereby substantially eliminating any induced load along the longitudinal axis of the specimen. The present device minimizes premature specimen loading, which, if of significant magnitude, could cause the specimen to yield or fail during gripping. In addition, the present device is generally symmetrical to eliminate front-to-back gripping force differentials across the grip jaws. This prevents any bending moment from being applied to the specimen and thus provides more accurate test results. Specimen grips of the present invention offer the further advantages of faster testing and processing time, since neither of the grips needs to be moved longitudinally along the specimen test axis in order to install a specimen. While a greater rate of specimen testing is possible with the specimen grips of the present invention, safety is not compromised for speed. The specimen grips of the present invention are safer than prior art grips because once set up for a particular size specimen, there is no need to move the grips longitudinally in order to place the specimen within the grips for testing. An operator simply slides the specimen from the side in between the grip jaws of the specimen grips and the grips are actuated to clamp specimen.
The assignee of the present application has sold grips such as those shown in U.S. Pat. No. 3,335,603, as Model Series 641 Hydraulically Operated Grips. These grips show horizontal or transverse gripping motion but the outer housing completely encloses the wedge arrangement, and they do not permit loading of specimens from the side. Additionally, said assignee has sold "Series 645 Mechanical Wedge Grips" for tension loading. These are mechanically actuated grips into which a specimen may be installed from one side only, and the wedges used for these grips tend to move vertically as they are locked onto the specimen. Another specimen testing grip is shown in U.S. Pat. No. 3,320,798, issued to Martin M. Gram, on May 23, 1967.